Villin

Barbed-end-capping proteins (gelsolin and villin, 95 kD) attach to this specific end of the actin filament and inhibit the further addition of actin molecules. 

Proteins that cross-link actin filaments bind to their sides to produce bundles or three-dimensional networks (Otto, 1994). In microvilli, approximately 20 actin filaments of the core are cross-linked by villin (95 kD) and fimbrin (68 kD) in helical array to form a compact bundle (Figure 5). Filamin (2 x 250 kD) induces the formation of an actin network with gel formation. By immunofluorescence microscopy, this ABP is found in the ruffled, motile edge of cultured cells, where only actin filaments are abundant. 

Bundles of parallel actin filaments with uniform polarity. The microvilli of intestinal epithelial cells (enterocytes) are packed with actin filaments that are attached to the overlying plasma membrane through a complex composed of a 110-kD protein and calmodulin. The actin filaments are attached to each other through fimbrin (68 kD) and villin (95 kD). The actin bundles that emerge out of the roots of microvilli disperse horizontally to form a filamentous complex, the terminal web, in which several cytoskeletal proteins, spectrin (fodrin), myosin, actinin, and tropomyosin are present. Actin in the terminal web also forms a peripheral ring, which is associated with the plasma membrane on the lateral surfaces of the enterocyte (see Figure 5, p. 24). 

Villin Vert. Fibroblast increased no apparent change Franck et al., 1990... 

Franck, Z., Footer, M., Bretscher, A. (1990). Microinjection of villin in cultured cells induces rapid and long-lasting changes in cell morphology but does not inhibit cytokinesis, cell motility or membrane ruffling. J. Cell Biol. Ill, 2475-2485. 

REX-CPHMD simulations have also been applied to understand the mechanism of the formation of protein intermediate states. Recent solution NMR data revealed a sparsely populated intermediate in the villin headpiece domain, in which the N-terminal subdomain is largely random but the C-terminal subdomain adopts a nativelike fold [34], Interestingly, H41 in this intermediate state titrates at a pH value of... 

Another interesting application area of PHMD simulations is to investigate electrostatic interactions in the unfolded states of proteins. A traditional view that unfolded proteins adopt random conformational states that are devoid of electrostatic and hydrophobic interactions, are recently challenged by experimental data [20, 69], REX-CPHMD folding simulations of the 35 residue C-terminal subdomain of the villin headpiece domain revealed a significant deviation from the standard pKa values for several titratable residues. Additional simulations, in which a charged group is neutralized confirmed the existence of specific electrostatic interactions in the unfolded states (JK and CLB, manuscript in preparation). 

Khandogin J, Raleigh DP, Brooks CL III (2007) Folding intermediate in the villin headpiece domain arises from disruption of a N-terminal hydrogen-bonded network. J Am Chem Soc 129 3056-3057. 

E., Brattain, M. G., Zweibaum, A., Epithelial polarity, villin expression, and enterocytic differentiation of cultured human colon carcinoma cells a survey of twenty cell lines, Cancer Res. 1988, 48, 1936-1942. 

George, S.P., Wang, Y., Mathew, S., Kamalakkannan, S., and Seema, K. (2007) Dimerization and actin-bundling properties of villin and its role in the assembly of epithelial cell brush borders. J. Biol. Chem. 10.1074/jbc.M703617200. 

GEL Sec23p and Sec24p Slime mold villin GEL PSI-BLAST (3) 6 X 10 4 A. thaliarm Sec23p... 

We extrapolate from two simulations, the 10 ps simulation on bovine pancreatic trypsin inhibitor (BPTI) reported over twenty years ago [61] and the recent 1 gs simulation on the villin headpiece subdomain. [9] Each of these was a state-of-the-art simulation, using the best algorithms and the most powerful hardware available at the time. 

An exact determination of the relative values of P for the BPTI and villin simulations is not possible, because some algorithmic developments reduce computational costs (particularly methods that allow one to increase the size of the time step and to efficiently treat long-range interactions), while others increase the costs (e.g., more detailed force fields and appropriate boundary conditions). But we can place reasonable bounds on the historical growth rate of P by using r=l and r=2 as lower and upper limits on the costs of calculating interatomic interactions. 

As in all computer applications for the past few decades, P has been growing exponentially with time. It is a straightforward calculation to show that in the 21 years between the BPTI simulation (t = KTns n 600) and the villin headpiece simulation (t = KT6 s n 12 000), P has been increasing by a factor of 10 every 3-4 years. A simple extrapolation would thus predict that a simulation covering the replication cyde of an intact E. coli with a volume of about 1 p3 (t 1000 s n=3x 1010) could be expected some time in the second half of the next century if computational power continued to grow exponentially at historical rates. 

Duan Y., Wang L. and Kouman P. A. The early stage of folding of villin headpiece sub-domain observed in a 200-nanosecond fully solvated molecular dynamics simulation. Proc. Natl. Acad. Sci., USA (1998) 95(17) 9897-9902. 

Fig. 7. Cartoon of villin 14T, based on the solution structure appearing in Refs. 302 and 305. Side chains constituting the two hydrophobic cores on either side of the central y8-sheet are shown. Reprinted with permission from Biochemistry, Vol. 37, S. E. Choe, P. T. Matsudaira, J. Osterhout, G. Wagner and E. I. Shakhnovich, 1998, p. 14,508. Copyright (1998) American Chemical Society.

De Mori, G.M.S., Colombo, G., Micheletti, C. Study of the villin headpiece folding dynamics by combining coarse-grained Monte Carlo evolution and all-atom molecular dynamics. Protein. Struct. Funct. Genet. 2005, 58, 459-71. 

Polymerization and depolymerization of actin, the main component of microfilaments, is controlled by a series of proteins, the activity of which is controlled by Ca and/or Ptdlns(4,5)P2. The Ca regulated proteins (see 6.7) are chiefly involved in processes of depolymerization of actin. Many of the proteins involved in the opposite process, actin polymerization, have specific binding sites for PtdIns(4,5)P2 and Ptlns(4)P and are regulated by the availability of phosphoinositides. Examples of such proteins are profilin, gelsolin, villin and talin (review Janmey, 1994). 

Bretscher, A., and K. Weber. 1979. Villin the major microfilament-associated protein of the intestinal microvillus. Proc Natl Acad Sci USA. 76 2321—5. 

Dabiri, G.A., C.L. Young, J. Rosenbloom, and F.S. Southwick. 1992. Molecular cloning of human macrophage capping protein cDNA. A unique member of the gelsolin/villin family expressed primarily in macrophages. J Biol Chem. 267 16545—52. 

Lee MR, Duan Y, Kollman PA (2000) Use of MM-PB/SA in estimating the free energies of proteins application to native, intermediates, and unfolded villin headpiece, Proteins, 39(4) 309-316... 

Carriere V, Lessufleur T, Barbat A et al. (1994) Expression of cy-tochrom P450 3A in HT-29-MTX cells and CACO-2 clone TC7. FEBS Letter 355 247-250 Chantret I, Barbat A, Dussaulx E et al. (1988) Epithelial polarity, villin expression, and enterocytic differentiation of cultured human colon carcinoma cells a survey of 20 cell-lines. Cancer Res 48 1936-1942 Cordon-Cardo C, O Brien JP, Boccia J et al. (1990) Expression of the multidrug resistance product (P-glycoprotein) in human normal and tumor tissues. J Histochem Cytochem 38 1277-1287... 

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